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Watts, Newton-Meters, Power & Torque - Making Sense of E-bike Motors

Black e-bike motor

If you’re considering shopping for an electric bike, power and torque are the two most common numbers to describe its performance. Electric bike power is typically measured in watts (W), whereas torque uses the Newton-meter (Nm) unit.

Power and torque affect the performance of all electric bike systems, whether you’re shopping for affordable electric bikes for commuting or high-performance Trek electric bikes. Understanding what these units mean and how they affect your e-bike’s capabilities will help you choose a model that best suits your needs.

How E-Bike Motors Work

The role of an electric bike motor is to provide electrically powered assistance. Unlike a moped, scooter or motorcycle, which feature independent throttles, an e-bike motor only delivers power when you pedal. 

The motor is powered using electric energy drawn from the battery, similar to a combustion engine powered by burning a fuel and air mixture. Depending on the motor’s specifications, it may generate varying amounts of maximum torque and power. 

The torque and power numbers determine the electric motor’s performance and overall capabilities, including maximum speed and pedal assist level on the road and when riding up inclines.

What is Torque?

Torque is a measurement of rotational force. In engines, it measures how hard the engine is turning. The more torque an e-bike motor has, the more force it can apply to the drivetrain. In broad terms, a higher torque propels the bike forward harder. 

All types of electric bikes benefit from better torque. A higher torque rating broadly translates into better acceleration, particularly from a standstill, making it an excellent feature for road electric bikes. Trek and trail e-bikes with more torque also have better hill-climbing performance.

What is Power?

Power is a measurement of energy. An engine power rating indicates the maximum amount of energy it can output. Engine power is calculated by multiplying the engine’s torque by the crankshaft’s angular speed.

For example, in motor vehicles, crankshaft speed corresponds to engine RPM, indicated by a tachometer. On electric bikes, the crankshaft’s speed depends on how fast the rider pedals and which gear the shifter is set to.

The more power an electric bike has, the more efficient the motor’s electric assistance and the less effort the rider needs to pedal. This benefit is especially noticeable when riding up hills and inclines. More power lets the e-bike handle higher loads without struggling, such as additional cargo or a passenger.

Legal Considerations of High Power Ratings

While higher engine power can theoretically translate into higher speeds, state and federal laws limit e-bike top speeds. For instance, most states have adopted a three-class system.

Class I and II models have a top speed of 20 mph, and Class III products have a top speed of 28 mph. Class II models may have either pedal or throttle assist, whereas Class I and III may only have pedal assist. Specific states also have additional restrictions, such as maximum engine power. For instance, the California Vehicle Code (CA VEH 312.5) defines an electric bicycle as any bicycle with an electric motor with a power rating of less than 750 W and “fully operable pedals.” 

Always review your local laws before choosing a high-powered Specialized or Stromer electric bike. Each state regulates e-bikes differently, and models classified as electric bikes in one jurisdiction may be classified as electric motorcycles or electric mopeds in another, which typically requires appropriate licensing and insurance.

How Power and Torque Ratings Affect Your Choice

You may be asking yourself, “Should I get an electric bike with high torque and power?” To answer this question, you must consider your needs and what applications your e-bike is intended to serve. 

Generally, the more powerful your electric motor, the more power it needs to draw from the battery, shortening its lifespan and decreasing its maximum range. If you need a fast, agile electric bike that can easily climb up hills or transport cargo, choosing a model with a more powerful electric motor will give you the performance you need on the road or the trail.

If range and longevity are a priority, look for lower-powered electric motors and long-lasting batteries. While an e-bike’s range is affected by multiple factors, including speed and pedal power, a less powerful motor will draw less power from the battery, and a higher number of Watt-hours (Wh) means the battery can hold more power before running out.

Find High-Performing Electric Bikes at Upway

Upway carries a wide selection of certified used electric bikes from the world’s most trusted manufacturers, such as Aventon, Bianchi, Cannondale, Gazelle, Giant, Pedego, Rad Power Bikes, or Specialized. 

Shop our catalog of pre-owned, professionally inspected e-bikes today. We will deliver our products to your doorstep anywhere in the lower 48 states within twelve business days.

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Upway offers the widest range of certified pre-owned electric bikes, reconditioned by professional mechanics. Thanks to Upway, you'll get a great electric bike at a price that's 20-60% off retail, with a one-year warranty!